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Tolerance of hypoxia is essential for most plants, but the underlying mechanisms are largely unknown. Here we show that adaptation to submergence induced hypoxia in Arabidopsis involves up-regulation of RAP2.2 through interactive action of WRKY33 and WRKY12. WRKY33- or WRKY12-overexpressing plants showed enhanced resistance to hypoxia. Y2H, BiFC, Co-IP and pull-down experiments confirmed the interaction of WRKY33 with WRKY12. Genetic experiments showed that RAP2.2 acts downstream of WRKY33/WRKY12. WRKY33 and WRKY12 can bind to and activate RAP2.2 individually. Genetic and molecular experiments demonstrate that the two WRKYs can synergistically enhance activation towards RAP2.2 to increase hypoxia tolerance. WRKY33 expression is increased in RAP2.2-overexpressing plants, indicating a feedback regulation by RAP2.2 during submergence process, which was corroborated by EMSA, ChIP, dual-LUC and genetic experiments. Our results show that a regulatory cascade module involving WRKY33, WRKY12 and RAP2.2 plays a key role in submergence induced hypoxia response of Arabidopsis and illuminate functions of WRKYs in hypoxia tolerance.

The Nobel Prize in Physiology or Medicine for the year 2019 has been awarded to three scientists, namely William G Kaelin, Gregg Semenza and Peter J Ratcliffe, for their research work leading to an understanding of the mechanism used by living cells to sense the level of O2. They discovered the occurrence of a molecule called hypoxia-inducible factor (HIF) within the cells and demonstrated that under normoxic condition, HIF undergoes hydroxylation and ubiquitination followed by its degradation in proteasome. Under conditions of hypoxia, HIF becomes active and binds to hypoxia response element available within hundreds of target genes leading to their activation to overcome the problems due to hypoxia. Any aberration in this process of degradation and activation of HIF may cause a variety of diseases, so drugs based on BIF stabilizers/inhibitors have been developed and are under different stages of clinical trials.

Background Cardiovascular diseases (CVDs) remain the leading cause of death worldwide. Hypoxia induces significant changes in cardiovascular control mechanisms potentially resulting in pathophysiology. Recently, an increasing number of long non-coding RNAs (lncRNAs) was reported to participate in the regulation of Hypoxia-inducible factors (HIF). Analysis of single-cell RNA-sequencing of human Abdominal Aortic Aneurysms pinpointed the endothelial-enriched lncRNA LINC01235. LINC01235 was previously correlated with tumour progression in gastric cancer and worse patient prognosis in breast cancer. Globally, the role of LINC01235 in the cardiovascular system remains unknown. Purpose The objective of this study is to unravel the function of LINC01235 in endothelial cells (ECs). Methods and results LINC01235 levels were elevated in human umbilical vein ECs (7.66 fold, p Conclusion In summary, the EC-enriched lncRNA LINC01235 is likely required for the suppression of hypoxia-induced gene expression under normoxic conditions potentially mediated by HIF-3α. Functionally, loss of LINC01235 decreased proliferation and VEGFA-stimulated angiogenic sprouting without an effect on cell death, metabolism or barrier integrity. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG - TRR267

Nearly 30 years ago hypoxia-inducible factor (HIF) was described as a protein complex bound to regulatory DNA sequences termed hypoxia response elements because HIF binding induced transcription of the erythropoietin gene under hypoxia. However, it soon became clear that HIF is part of a ubiquitous cellular oxygen sensing system, which ensures finely tuned control of HIF abundance and activity in dependence of the cellular oxygen tension. For their discoveries of how cells sense and adapt to oxygen availability Gregg L. Semenza, William G. Kaelin Jr. and Sir Peter J. Ratcliffe received the Nobel Prize in Physiology or Medicine 2019. The Nobel laureates' pioneering work on cellular oxygen sensing has unraveled that HIF has numerous target genes reflecting its multiple functions in cellular metabolism and adaptation to different levels of oxygen. Importantly, HIF is also crucial for the development of the nervous system. HIF has an influence on different neural cell types regarding neurogenesis, maturation and apoptosis. Furthermore, HIF is involved in pathophysiological processes of the brain like stroke and Alzheimer's disease resulting in the development of HIF-related therapeutic approaches.

Hypoxia-inducible factor (HIF), an αβ dimer, is the master regulator of oxygen homeostasis with hundreds of hypoxia-inducible target genes. Three HIF isoforms differing in the oxygen-sensitive α subunit exist in vertebrates. While HIF-1 and HIF-2 are known transcription activators, HIF-3 has been considered a negative regulator of the hypoxia response pathway. However, the humanHIF3AmRNA is subject to complex alternative splicing. It was recently shown that the long HIF-3α variants can form αβ dimers that possess transactivation capacity. Here, we show that overexpression of the long HIF-3α2 variant induces the expression of a subset of genes, including the erythropoietin (EPO) gene, while simultaneous downregulation of all HIF-3α variants by siRNA targeting a sharedHIF3Aregion leads to downregulation ofEPOand additional genes. EPO mRNA and protein levels correlated withHIF3Asilencing and HIF-3α2 overexpression. Chromatin immunoprecipitation analyses showed that HIF-3α2 binding associated with canonical hypoxia response elements in the promoter regions ofEPO. Luciferase reporter assays showed that the identified HIF-3α2 chromatin-binding regions were sufficient to promote transcription by all three HIF-α isoforms. Based on these data, HIF-3α2 is a transcription activator that directly regulatesEPOexpression.

Environmental stressors, such as warm temperatures and hypoxia, can interact and pose a threat to aquatic species. Cross talk between the hypoxia and heat stress cellular pathways can lead to enhanced cross tolerance between these environmental stressors. In this study, we questioned whether elevated temperatures (from 27° to 32°C) during rearing would enhance the hypoxia-inducible transcription factor-1 (HIF-1)-mediated transcriptional response to hypoxia (5% dissolved O

Factor inhibiting hypoxia-inducible factor (FIH) is a JmjC domain 2-oxogluarate and Fe(II)-dependent oxygenase that catalyzes hydroxylation of specific asparagines in the C-terminal transcriptional activation domain of hypoxia-inducible factor alpha (HIF-α) isoforms. This modification suppresses the transcriptional activity of HIF by reducing its interaction with the transcriptional coactivators p300/CBP. By contrast with inhibition of the HIF prolyl hydroxylases (PHDs), inhibitors of FIH, which accepts multiple non-HIF substrates, are less studied; they are of interest due to their potential ability to alter metabolism (either in a HIF-dependent and/or -independent manner) and, provided HIF is upregulated, to modulate the course of the HIF-mediated hypoxic response. Here we review studies on the mechanism and inhibition of FIH. We discuss proposed biological roles of FIH including its regulation of HIF activity and potential roles of FIH-catalyzed oxidation of non-HIF substrates. We highlight potential therapeutic applications of FIH inhibitors.

The cell cycle is an important cellular process whereby the cell attempts to replicate its genome in an error-free manner. As such, mechanisms must exist for the cell cycle to respond to stress signals such as those elicited by hypoxia or reduced oxygen availability. This review focuses on the role of transcriptional and post-transcriptional mechanisms initiated in hypoxia that interface with cell cycle control. In addition, we discuss how the cell cycle can alter the hypoxia response. Overall, the cellular response to hypoxia and the cell cycle are linked through a variety of mechanisms, allowing cells to respond to hypoxia in a manner that ensures survival and minimal errors throughout cell division.

ER-mitochondria contacts respond to cellular stress. Chai et al. reveal that in response to hypoxia, USP19, an ER-resident deubiquitinase, accumulates at ER-mitochondria contact sites where USP19 deubiquitinates and stabilizes FUNDC1, thereby promoting Drp1 oligomerization and subsequent hypoxia-induced mitochondria division., The ER tethers tightly to mitochondria and the mitochondrial protein FUNDC1 recruits Drp1 to ER-mitochondria contact sites, subsequently facilitating mitochondrial fission and preventing mitochondria from undergoing hypoxic stress. However, the mechanisms by which the ER modulates hypoxia-induced mitochondrial fission are poorly understood. Here, we show that USP19, an ER-resident deubiquitinase, accumulates at ER-mitochondria contact sites under hypoxia and promotes hypoxia-induced mitochondrial division. In response to hypoxia, USP19 binds to and deubiquitinates FUNDC1 at ER-mitochondria contact sites, which facilitates Drp1 oligomerization and Drp1 GTP-binding and hydrolysis activities, thereby promoting mitochondrial division. Our findings reveal a unique hypoxia response pathway mediated by an ER protein that regulates mitochondrial dynamics.

Hypoxia-inducible transcription factors (HIFs) are fundamental to the cellular adaptation to low oxygen levels but how they interact with chromatin and efficiently activate their target genes is unclear. Using genome-wide mutagenesis in human cancer cells, we define genes required for HIF transcriptional activation, and identify a requirement for the Histone 3 lysine 4 (H3K4) methyltransferase SET1B. Loss of SET1B leads to a selective reduction in HIF transcriptional activity in hypoxia, with SET1B driving expression of genes involved in angiogenesis rather than glycolysis, resulting in impaired tumour establishment in SET1B deficient xenografts. Mechanistically, we show that SET1B is itself oxygen regulated, accumulates on chromatin in hypoxia, and is recruited to HIF target genes through HIF-1α. Accordingly, we show that the hypoxic induction of H3K4me3 at specific HIF targets is both HIF and SET1B dependent, and when impaired, decreases promoter acetylation and gene expression. Together, these findings reveal SET1B as a determinant of site-specific histone methylation and provide insight into how HIF target genes are differentially regulated.

Sugar supply is a key component of hypoxia tolerance and acclimation in plants. However, a striking gap remains in our understanding of mechanisms governing sugar impacts on low-oxygen responses. Here, we used a maize (Zea mays) root-tip system for precise control of sugar and oxygen levels. We compared responses to oxygen (21 and 0.2%) in the presence of abundant versus limited glucose supplies (2.0 and 0.2%). Low-oxygen reconfigured the transcriptome with glucose deprivation enhancing the speed and magnitude of gene induction for core anaerobic proteins (ANPs). Sugar supply also altered profiles of hypoxia-responsive genes carrying G4 motifs (sources of regulatory quadruplex structures), revealing a fast, sugar-independent class followed more slowly by feast-or-famine-regulated G4 genes. Metabolite analysis showed that endogenous sugar levels were maintained by exogenous glucose under aerobic conditions and demonstrated a prominent capacity for sucrose re-synthesis that was undetectable under hypoxia. Glucose abundance had distinctive impacts on co-expression networks associated with ANPs, altering network partners and aiding persistence of interacting networks under prolonged hypoxia. Among the ANP networks, two highly interconnected clusters of genes formed around Pyruvate decarboxylase 3 and Glyceraldehyde-3-phosphate dehydrogenase 4. Genes in these clusters shared a small set of cis-regulatory elements, two of which typified glucose induction. Collective results demonstrate specific, previously unrecognized roles of sugars in low-oxygen responses, extending from accelerated onset of initial adaptive phases by starvation stress to maintenance and modulation of co-expression relationships by carbohydrate availability.

The von Hippel–Lindau protein (pVHL) is a tumour suppressor mainly known for its role as master regulator of hypoxia-inducible factor (HIF) activity. Functional inactivation of pVHL is causative of the von Hippel–Lindau disease, an inherited predisposition to develop different cancers. Due to its impact on human health, pVHL has been widely studied in the last few decades. However, investigations mostly focus on its role in degrading HIFs, whereas alternative pVHL protein–protein interactions and functions are insistently surfacing in the literature. In this review, we analyse these almost neglected functions by dissecting specific conditions in which pVHL is proposed to have differential roles in promoting cancer. We reviewed its role in regulating phosphorylation as a number of works suggest pVHL to act as an inhibitor by either degrading or promoting downregulation of specific kinases. Further, we summarize hypoxia-dependent and -independent pVHL interactions with multiple protein partners and discuss their implications in tumorigenesis.

In the field of toxicology or environmental science, some researchers are wondering a question. That is, whether specific molecular signaling pathways in response to certain environmental toxicants or stresses exist in organisms. We selected three well-described response signals (heavy metal response, heat shock response, and hypoxia response) to discuss this question. So far, the obtained knowledge does not support the possible existence of specific molecular signaling pathways in response to certain environmental toxicants or stresses at least in nematodes.

Hypoxia is an important stress for organisms, including plants and mammals. In plants, hypoxia can be the consequence of flooding and causes important crop losses worldwide. In mammals, hypoxia stress may be the result of pathological conditions. Understanding the regulation of responses to hypoxia offers insights into novel approaches for crop improvement, particularly for the development of flooding-tolerant crops and for producing better therapeutics for hypoxia-related diseases such as inflammation and cancer. Despite their evolutionary distance, plants and mammals deploy strikingly similar mechanisms to sense and respond to the different aspects of hypoxia-related stress, including low oxygen levels and the resulting energy crisis, nutrient depletion, and oxidative stress. Over the last two decades, the ubiquitin/proteasome system and the ubiquitin-like protein SUMO have been identified as key regulators that act in concert to regulate core aspects of responses to hypoxia in plants and mammals. Here, we review ubiquitin and SUMO-dependent mechanisms underlying the regulation of hypoxia response in plants and mammals. By comparing and contrasting these mechanisms in plants and mammals, this review seeks to pinpoint conceptually similar mechanisms but also highlight future avenues of research at the junction between different fields of research.

Cells experience different oxygen concentrations depending on location, organismal developmental stage, and physiological or pathological conditions. Responses to reduced oxygen levels (hypoxia) rely on the conserved hypoxia-inducible factor 1 (HIF-1). Understanding the developmental and tissue-specific responses to changing oxygen levels has been limited by the lack of adequate tools for monitoring HIF-1 in vivo. To visualise and analyse HIF-1 dynamics in Drosophila, we used a hypoxia biosensor consisting of GFP fused to the oxygen-dependent degradation domain (ODD) of the HIF-1 homologue Sima. GFP-ODD responds to changing oxygen levels and to genetic manipulations of the hypoxia pathway, reflecting oxygen-dependent regulation of HIF-1 at the single-cell level. Ratiometric imaging of GFP-ODD and a red-fluorescent reference protein reveals tissue-specific differences in the cellular hypoxic status at ambient normoxia. Strikingly, cells in the larval brain show distinct hypoxic states that correlate with the distribution and relative densities of respiratory tubes. We present a set of genetic and image analysis tools that enable new approaches to map hypoxic microenvironments, to probe effects of perturbations on hypoxic signalling, and to identify new regulators of the hypoxia response., Biology Open, 6 (2), ISSN:2046-6390

Among the complex and articulated molecular mechanisms activated by hypoxia, microRNAs play a central role. Specifically, this Forum is dedicated to hypoxamiRs, defined as microRNAs that not only are directly regulated by hypoxia but also regulate cell responses to decreased oxygen tension. We assembled a collection of reviews and research communications by authoritative leaders in a variety of disciplines, describing hypoxamiRs from different angles. Fundamental technical issues as well as hypoxamiR impact on general events, such as metabolism and development, are critically reviewed. The regulation and the role of hypoxamiRs in cardiovascular diseases and in cancer are also addressed. An increased understanding of the function of hypoxamiR in gene regulatory networks of great physiopathological relevance may allow the development of innovative therapeutic approaches for all ischemic diseases. Antioxid. Redox Signal. 21, 1164–1166.

MicroRNAs (miRs) are short non-coding transcripts involved in a wide variety of cellular processes. Several recent studies have established a link between hypoxia, a well-documented component of the tumour microenvironment, and specific miRs. One member of this class, miR-210, was identified as hypoxia inducible in all the cell types tested, and is overexpressed in most cancer types. Its hypoxic induction is dependent on a functional hypoxia-inducible factor (HIF), thus extending the transcriptional repertoire of the latter beyond ‘classic’ genes. From a clinical standpoint, miR-210 overexpression has been associated with adverse prognosis in breast tumours and been detected in serum of lymphoma patients and could serve as a tool to define hypoxic malignancies. We discuss the role of miR-210 and its emerging targets, as well as possible future directions for clinical applications in oncology and ischaemic disorders.

We identified MafG as a protein that interacts with HIF-1α, a key factor in hypoxic response, using the yeast two-hybrid system. Interaction between MafG and HIF-1α was confirmed by surface plasmon resonance and by translocation to the nucleolus with the NoLS signal. A knockdown of MafG reduced erythropoietin (EPO) mRNA levels as well as luciferase reporter activity with the hypoxia response element. The knockdown of MafG did not change total HIF-1α protein, but reduced the accumulation of HIF-1α in the nuclei. These results suggest that MafG regulates the hypoxic response of cells by detaining HIF-1α in the nuclei.Structured summaryMINT-6550898:HIF1A (uniprotkb:Q16665) physically interacts (MI:0218) with MAFG (uniprotkb:Q9BRP3) by two hybrid (MI:0018)MINT-6550966:HIF1A (uniprotkb:Q16665) physically interacts (MI:0218) with HSP90 alpha (uniprotkb:P07900) by surface plasmon resonance (MI:0107)MINT-6550948:HIF1A (uniprotkb:Q16665) physically interacts (MI:0218) with MAFK (uniprotkb:A5PLQ5) by surface plasmon resonance (MI:0107)MINT-6550925:HIF1A (uniprotkb:Q16665) physically interacts (MI:0218) with MAFG (uniprotkb:Q9BRP3) by surface plasmon resonance (MI:0107)MINT-6550912:MAFG (uniprotkb:Q9BRP3) and HIF1A (uniprotkb:Q16665) physically interact (MI:0218) by fluorescence microscopy (MI:0416)MINT-6550980:HIF1A (uniprotkb:Q16665) physically interacts (MI:0218) with HSP90 beta (uniprotkb:P08238) by surface plasmon resonance (MI:0107)

Hypoxia-inducible factor-1 (HIF-1), a heterodimeric (containing α and β subunits) transcription factor, is involved in hypoxia response pathway that regulates the expression of many tumorrelated genes. The stabilized HIF-1 heterodimer couples to the general co-activators p300/CBP (CREB binding protein), forming an active transcription factor to initiate hypoxic responses. Inhibiting the transcription factor-coactivator HIF-1α-p300/CBP interaction represents an attractive approach for blocking hypoxia pathway in tumors. Recently, diverse HIF-1α-p300/CBP inhibitors have been designed and their anti-tumor activities have been evaluated. The developments of inhibitors of HIF-1α- p300/CBP are discussed in this review. An outline of structures and biological activities of these inhibitors can be traced, along with the approaches for inhibitors discovery. The challenges in identifying novel and selective potent inhibitors of HIF-1α-p300/CBP are also put forward.

Jujubae Fructus, known as jujube or Chinese date, is the fruit of Ziziphus jujuba (Mill.), which not only serves as daily food, but acts as tonic medicine and health supplement for blood nourishment and sedation. According to Chinese medicine, jujube is commonly included in herbal mixtures, as to prolong, enhance and harmonize the efficiency of herbal decoction, as well as to minimize the toxicity. Here, we aim to compare the chemical and pharmacological properties of three commonly used jujube-containing decoctions, including Guizhi Tang (GZT), Neibu Dangguijianzhong Tang (NDT) and Zao Tang (ZOT). These decoctions share common herbs, i.e. Glycyrrhizae Radix et Rhizoma Praeparata cum Melle, Zingiberis Rhizoma Recens and Jujube, and they have the same proposed hematopoietic functions. The amount of twelve marker biomolecules deriving from different herbs in the decoctions were determined by LC-MS, and which served as parameters for chemical standardization. In general, three decoctions showed common chemical profiles but with variations in solubilities of known active ingredients. The chemical standardized decoctions were tested in cultured Hep3B cells. The herbal treatment stimulated the amount of mRNA and protein expressions of erythropoietin (EPO) via the activation of hypoxia response elements: the three herbal decoctions showed different activation. The results therefore demonstrated the hematopoietic function of decoctions and explained the enhancement of jujube function within a herbal mixture.

OASIS/CREB3L1 (Old astrocyte specifically induced substance), an endoplasmic reticulum (ER)–resident transcription factor, plays important roles in differentiation of osteoblasts and astrocytes. OA...

The ability to sense and respond to stressful conditions is essential to maintain organismal homeostasis. It has long been recognized that stress response factors that improve survival in changing conditions can also influence longevity. In this review, we discuss different strategies used by animals in response to decreased O(2) (hypoxia) to maintain O(2) homeostasis, and consider interactions between hypoxia responses, nutritional status, and H(2)S signaling. O(2) is an essential environmental nutrient for almost all metazoans as it plays a fundamental role in development and cellular metabolism. However, the physiological response(s) to hypoxia depend greatly on the amount of O(2) available. Animals must sense declining O(2) availability to coordinate fundamental metabolic and signaling pathways. It is not surprising that factors involved in the response to hypoxia are also involved in responding to other key environmental signals, particularly food availability. Recent studies in mammals have also shown that the small gaseous signaling molecule hydrogen sulfide (H(2)S) protects against cellular damage and death in hypoxia. These results suggest that H(2)S signaling also integrates with hypoxia response(s). Many of the signaling pathways that mediate the effects of hypoxia, food deprivation, and H(2)S signaling have also been implicated in the control of lifespan. Understanding how these pathways are coordinated therefore has the potential to reveal new cellular and organismal homeostatic mechanisms that contribute to longevity assurance in animals.

Cell invasion and metastasis mark the most lethal phase of cancer, but little is known about the key molecular events that initiate this crucial turning point. Low oxygen, or hypoxia, is thought to be one trigger for metastasis. Hypoxic conditions within the tumor mass are thought to activate signaling pathways that stimulate invasiveness of cancer cells spreading the disease. However, the molecular basis of this process is not well understood. A recent study used Drosophila ovarian border cell migration to model the type of cell migration that occurs in tumors in response to oxygen deprivation through the activation of the hypoxia response pathway (Doronkin et al. Oncogene. 2009). This model organism approach revealed a highly sophisticated mechanism of control of cell migration that is regulated by multiple genetic inputs tied to the hypoxic response. Genetic manipulations with the components of the HIF-1 (hypoxia-inducible factor 1) pathway were able to either inhibit or block the migration of border cells or cause unprecedented acceleration of their migration. The HIF-1-mediated transcriptional cascade appears to be the major regulator of border cell locomotion. Based on the similarity of the fly and human HIF-1 pathways, this model organism study might lead to improvements in understanding hypoxia-induced metastasizing of human cancers. This article discusses new findings in the context of their relevance to cancer metastasis and speculates on the potential regulatory mechanisms and future research directions.

Plants need oxygen, but they don’t always get enough of it. Under waterlogging or other hypoxic conditions, oxygen is not available to act as an electron acceptor in the oxidative phosphorylation pathway. ATP production plummets, depriving the plant of the energy it needs to survive. Fortunately

A complex bioregulatory network could be more easily comprehended if its essential function could be described by a small “core” subsystem, and if its response characteristics were switch-like. We tested this proposition by simulation studies of the hypoxia response control network. We hypothesized that a small subsystem governs the basics of the cellular response to hypoxia and that this response has a sharp oxygen-dependent transition. A molecular interaction map of the network was prepared, and an evolutionarily conserved core subsystem was extracted that could control the activity of hypoxia response promoter elements on the basis of oxygen concentration. The core subsystem included the hypoxia-inducible transcription factor (HIFα:ARNT heterodimer), proline hydroxylase, and the von Hippel-Lindau protein. Simulation studies showed that the same core subsystem can exhibit switch-like responses both to oxygen level and to HIFα synthesis rate, thus suggesting a mechanism for hypoxia response promoter element-dependent responses common to both hypoxia and growth factor signaling. The studies disclosed the mechanism responsible for the sharp transitions. We show how parameter sets giving switch-like behavior can be found and how this type of behavior provides a foundation for quantitative studies in cells.

International audience; Expression of vascular endothelial growth factor (VEGF) by cultured vascular smooth muscle cells was analyzed. Serum and hypoxia had nearly additive actions on VEGF mRNA expression. The function of the VEGF promoter in smooth muscle cells was analyzed using transient luciferase reporter assays. Serum and hypoxia stimulated expression of luciferase. The presence of hypoxia response element (HRE) was necessary for the hypoxic induction. AP-1 sequences located upstream of HRE and AP-2/Sp-1 sequences located downstream of HRE are not necessary. Hypoxic responses were best observed in serum-deprived cells. They were largely absent in serum-stimulated cells. Serum did not suppress the hypoxic response by interfering with the hypoxia sensor mechanism or with the signaling cascade that leads to the activation of HIF-1. It is concluded that growth-promoting cytokines regulate hypoxic gene induction in smooth muscle cells.

The recent discovery of molecules that mediate the hypoxia response pathway demonstrates that mammalian cells are supremely well adapted to dealing with conditions of low oxygen. In their Perspective, [Bruick and McKnight][1] detail new findings ([ Lando et al .][2]) that describe an additional way in which the transcription factor HIF, a central player in the hypoxia response pathway, can be regulated. [1]: http://www.sciencemag.org/cgi/content/full/295/5556/807 [2]: http://www.sciencemag.org/cgi/content/short/295/5556/858

Understanding the resistance of glioma cells to chemotherapy has been an enormous challenge. In particular, mechanisms by which tumor cells acquire resistance to chemotherapy under hypoxic conditions are not fully understood. In this study, we have found that miR-497 is overexpressed in glioma and that hypoxia can induce the expression of miR-497 at the transcriptional level by binding with the hypoxia response element in the promoter. Ectopic overexpression of miR-497 promotes chemotherapy resistance in glioma cells by targeting PDCD4, a tumor suppressor that is involved in apoptosis. In contrast, the inhibition of miR-497 enhances apoptosis and increases the sensitivity of glioma cells to TMZ. These results suggest that miR-497 is a potential molecular target for glioma therapy.

We thank Vooijs et al. for their interest and comments about our paper.1 Vooijs et al. had found that hypoxia induces Twist1 expression in a hypoxia-inducible factor (HIF)-2-dependent manner and that intronic hypoxia response elements of Twist1 are regulated by HIF-2.2 In our study, direct transcriptional activation of Twist by HIF-1 was found to promote epithelial-to-mesenchymal transition (EMT) in tubular cells.3 Yang et al.4 also showed that HIF-1 directly regulates the expression of Twist by binding to hypoxia-responsive elements in the Twist proximal promoter, resulting in EMT and metastastic phenotypes. Thus, Twist may be the target gene of both HIF-1 and HIF-2. However, we think the role of Twist in hypoxia-induced renal EMT and fibrosis is mediated only by HIF-1, not HIF-2.

Background Hypoxia is associated with many disease conditions in humans, such as cancer, stroke and traumatic injuries. Hypoxia elicits broad molecular and cellular changes in diverse eukaryotes. Our recent studies suggest that one likely mechanism mediating such broad changes is through changes in the cellular localization of important regulatory proteins. Particularly, we have found that over 120 nuclear proteins with important functions ranging from transcriptional regulation to RNA processing exhibit altered cellular locations under hypoxia. In this report, we describe further experiments to identify and evaluate the role of nuclear protein relocalization in mediating hypoxia responses in yeast. Results To identify regulatory proteins that play a causal role in mediating hypoxia responses, we characterized the time courses of relocalization of hypoxia-altered nuclear proteins in response to hypoxia and reoxygenation. We found that 17 nuclear proteins relocalized in a significantly shorter time period in response to both hypoxia and reoxygenation. Particularly, several components of the SWI/SNF complex were fast responders, and analysis of gene expression data show that many targets of the SWI/SNF proteins are oxygen regulated. Furthermore, confocal fluorescent live cell imaging showed that over 95% of hypoxia-altered SWI/SNF proteins accumulated in the cytosol in hypoxic cells, while over 95% of the proteins were nuclear in normoxic cells, as expected. Conclusions SWI/SNF proteins relocalize in response to hypoxia and reoxygenation in a quick manner, and their relocalization likely accounts for, in part or in whole, oxygen regulation of many SWI/SNF target genes.